Low sulfur motor gasoline (mogas) requires the production of low sulfur blend stocks for the mogas pool. The primary blend stocks are derived from cat cracked (e.g., FCC) naphthas, which in addition to unwanted organic sulfur compounds, are rich in olefins desirable for meeting high octane rating requirements. The naphtha is reacted with hydrogen in the presence of a sulfided hydrodesulfurization (HDS) catalyst, which results in the formation of H2S and a sulfur-reduced naphtha. The H2S is separated from the sulfur-reduced naphtha, which naphtha is then used for mogas. HDS catalysts are known and typically contain a catalytic component of at least one Group VIB metal, and more often a mixture of non-noble Group VIII and Group VIB metals. In addition to having catalytic activity for removing sulfur and other heteroatoms, these naphtha hydrodesulfurization catalysts have hydrogenation activity, which saturates desirable olefins.
Conventional fixed bed hydrodesulfurization can reduce the sulfur level of cracked naphthas to very low levels; however, it typically also results in undesirable octane loss because of excessive hydrogenation of olefins. Further, H2S produced during conventional hydrodesulfurization, reacts with olefins in the feed to form mercaptans, which are known as reversion mercaptans. A process, referred as SCANfining, has been developed which employs a proprietary catalyst that avoids the undesirable degree of octane loss through olefin saturation. Such a process and catalysts are taught in U.S. Pat. Nos. 6,013,598; 6,231,753; 6,913,688 and 7,220,352.